Process for the production of soap from neutral fats

ABSTRACT

A process for the production of soap from neutral fats by reaction of fats and/or oils with an alkaline hydroxide or a mixture of alkaline hydroxides, consisting in reacting, at a temperature exceeding 100° C. and under pressure an aqueous solution of the alkaline hydroxide or a mixture of alkaline hydroxides, having a quantity in moles of hydroxide substantially equal to the one of the fatty acids contained in the fat and/or oil and a quantity of water equal to the one necessary to obtain the required concentration of fatty acids in the final soap heated at a sufficient temperature to obtain a clear solution, with the fat and/or oil previously heated at a temperature at least equal to the one of the aqueous solution of the alkaline hydroxide.

DESCRIPTION

[0001] The present invention relates to a process for the production ofsoap from neutral fats.

[0002] More particularly, the present invention relates to a process forthe direct production of soap from neutral fats having the requiredconcentration of fatty acids, without the intermediate production of asoap having a lower concentration of fatty acids and the subsequentconcentration to reach the requested percentage of said fatty acids.

[0003] The process according to the present invention is particularlysuitable for the direct production of soaps having a high concentrationof fatty acids, for example exceeding 63% by weight.

[0004] The term “concentration of fatty acids”, as it is used in thepresent description and claims, is a conventional way to express theconcentration of active fat material which represents in a sense the“washing power” of a soap.

[0005] As it is known, soaps are alkaline salts of higher fatty acidssuch as oleic, stearic, palmitic and laurilic, etc. acids contained inthe form of triglycerides in natural fat substances of vegetable andanimal origin. They are obtained by reaction of fats and oils with astrong inorganic base, generally sodium hydroxide sometimes substitutedor in mixture with potassium hydroxide.

[0006] The result of the reaction between neutral fats or oils andalkaline hydroxide is a mixture of soap, glycerine, (residue of thetriglycerides splitting in fatty acids), water and all impuritiescontained in reagents.

[0007] According to the known processes, for the elimination of possibleimpurities, the thus obtained product is subjected to a washing processwhich is carried out by dilution with water and subsequent separation ofthe soap by the addition of an electrolyte (NaCl, another salt or sodiumhydroxide), being the soap insoluble in electrolyte solutions over adetermined concentration. The most of water soluble impurities andglycerine are eliminated from the soap by the washing waters.

[0008] In common processes for the production of soaps, the sodiumhydroxide is fed by an aqueous solution and its concentration isgenerally lower than about 50%; in fact, aqueous solutions having ahigher concentration, at room temperature, show an insoluble bottommaterial. Moreover, with concentrated hydroxide solutions whose limitdepends on the kind of fat or oil used, at atmospheric pressure, thesaponification reaction does not start up.

[0009] With the known processes, the obtained washed soap has aconcentration of fatty acids which is not exceeding 62-63% by weight.

[0010] In order to obtain a soap with a higher concentration, such aslaundry soap, having a concentration of fatty acids of about 72%, ortoilet soap, having a concentration of fatty acids of about 78%-80%, itis necessary to subject the saponification product, after washing, to aconcentration process.

[0011] The concentration process consists in heating under pressure thehot and liquid soap, coming from the washing phase, at about 80-90° C.and subsequently in spraying the hot under pressure soap in a vacuumchamber. During this operation, the soap loses part of the water,cooling and concentrating at the same time. When coming out of thevacuum concentration plant, the soap, at atmospheric pressure, is in theform of a plastic mass at a temperature of about 30-40° C.

[0012] Even though this process is commonly used in industry, it showssome drawbacks, which are mainly due to the vacuum itself. In fact, forits processing, the vacuum plant needs a very high vacuum of some mm ofHg, this greatly affects running and ownership costs, moreover itinvolves operation and maintenance problems.

[0013] Another drawback, which is always due to the vacuum concentrationprocess, is the formation of the so-called “dry specks”. In fact, duringthe free expansion of soap, generally going from 2 bars to few mm of Hg,overdried particles of soap called “dry specks” are formed conferringthe sandy sensation found in some kinds of soap if a proper treatment toremove said particles is not carried out.

[0014] Object of the present invention is to avoid the above mentioneddrawbacks.

[0015] More particularly, object of the present invention is to providea saponification process from neutral fats that allows the directproduction of a soap, which does not require a further concentration.

[0016] A further object of the present invention is to provide asaponification process from neutral fats that allows the directproduction of a soap with a concentration of fatty acids having therequired concentration of fatty acids, even exceeding 63% and up to78-80%.

[0017] According to the present invention this and other objects whichwill result from the description, are obtained by a process for theproduction of soap from neutral fats by reaction of fats and/or oilswith an alkaline hydroxide or a mixture of alkaline hydroxides, saidprocess consists in:

[0018] preparing an aqueous solution of the alkaline hydroxide or amixture of alkaline hydroxides having a quantity of hydroxide in moleswhich is substantially equal to one of the fatty acids contained in thefat and/or oil, and a quantity of water equal to the one necessary toobtain the required concentration of the fatty acids in the final soap;

[0019] heating the thus obtained aqueous solution at a sufficienttemperature to obtain a clear solution of the alkaline hydroxide;

[0020] heating the fat and/or oil at a temperature at least equal to theone of the alkaline hydroxide aqueous solution;

[0021] mixing the hot and liquid fat and/or oil with the hot aqueoussolution of the alkaline hydroxide in a pressure reactor, and

[0022] completing the reaction at a temperature exceeding 100° C. andunder pressure.

[0023] The hot and under pressure reaction mass thus obtained is thencooled in the form of blocks, noodles or bars.

[0024] The aqueous solution of the alkaline hydroxide or mixture ofalkaline hydroxides is preferably heated at a temperature exceeding 50°C. and more preferably at a temperature between 90 and 150° C.,depending on the hydroxide concentration. Therefore, for example, anaqueous solution containing about 0.305 kmoles of NaOH and about 5.95 kgof water is clear at 110° C., and a solution containing about 0.312kmoles of NaOH and about 3.55 kg of water is clear at 150° C.

[0025] The saponification reaction is preferably carried out at atemperature between 110 and 160° C. and at pressure between 2 and 4bars.

[0026] In order to increase the soap fluidity, sodium chloride or anelectrolyte can be added to the alkaline hydroxide aqueous solution; theconcentration of sodium chloride or electrolyte can vary between 0.1 and0.5% by weight with respect to the soap.

[0027] As above said, the aqueous solution added to the saponificationreactor contains a number of moles of alkaline hydroxide or mixture ofalkaline hydroxides which is substantially equal to the one of the fattyacids contained in the fat and/or oil to be saponified and a quantity ofwater equal to the one needed to obtain the required concentration offatty acids in the final soap.

[0028] Therefore, for instance, in order to obtain a soap having a totalamount of fatty acids of about 78% by weight, from a mixture of neutralfats consisting in 80% by weight of tallow and in 20% by weight incoconut oil, according to the process of the present invention

[0029] 65.49 kg of tallow;

[0030] 16.37 kg of coconut oil;

[0031] an aqueous solution of a sodium hydroxide consisting of 12.19 kgof NaOH at 100% (=0.305 kmoles) and 5.95 kg of water heated at 110° C.are used.

[0032] The mixture of neutral fats is heated at 120° C. andsaponification is carried out at 120-140° C. under pressure.

[0033] The thus obtained soap is constituted by:

[0034] 84.70 kg of anhydrous soap;

[0035] 9.34 kg of glycerine;

[0036] 5.96 kg of water

[0037] Any fat and natural oil of vegetable and/or animal origin can beused in the process of the present invention. If necessary, fats andoils can be previously subjected to a bleaching and deodorizationprocess according to the required pureness of the final soap.

[0038] The process can be batch way or continuously carried out. Thehot, under pressure product coming from the saponification reaction issubjected to cooling in continuous or batch way processes in order toobtain soap in the form of blocks, noodles or bars. Any device and/orprocess, which are well known to this purpose, can be used.

[0039] From the above description, the advantages obtained by theprocess of the present invention are evident. They consist in obtainingthe soap with the required concentration of fatty acids directly fromthe saponification reaction, thus avoiding further washing andconcentration processes with all the relating problems concerning plant,maintenance, cost and “dry specks” in the final product.

[0040] Moreover, the process of the present invention allows theobtaining of a soap with a high concentration of fatty acids, such as78-80% that could not be directly obtained with the known saponificationprocesses up to now.

1. A process for the production of soap from neutral fats by reaction offats and/or oils with an alkaline hydroxide or mixture of alkalinehydroxides, characterized by the fact that this process consists in:preparing an aqueous solution of the alkaline hydroxide or mixture ofalkaline hydroxides having a quantity in moles equal to the one of thefatty acids contained in the fat and/or oil and a quantity of waterequal to the one required to obtain the required concentration of fattyacids in the final soap; heating the thus obtained aqueous solution at asufficient temperature to obtain a clear solution of the alkalinehydroxide; heating the fat and/or oil at a temperature at least equal tothe one of the alkaline hydroxide aqueous solution; mixing the hot andliquid fat and/or oil with the hot aqueous solution of the alkalinehydroxide in a pressure reactor and, completing the reaction underpressure at a temperature exceeding 100° C.
 2. The process for theproduction of soap according to claim 1 , wherein the hot and underpressure reaction mass, coming from the reactor, is cooled in the shapeof blocks, noodles or bars.
 3. The process for the production of soapaccording to claim 1 or 2 , wherein the aqueous solution of the alkalinehydroxide or mixture of alkaline hydroxides is heated at a temperatureexceeding 50° C.
 4. The process for the production of soap according toclaim 3 , wherein the aqueous solution of the alkaline hydroxide ormixture of alkaline hydroxides is heated at a temperature between 90 and150° C.
 5. The process for the production of soap according to any ofthe preceding claims, wherein the saponification reaction is carried outat a temperature between 110 and 160° C. and at a pressure between 2 and4 bar.
 6. The process for the production of soap according to any one ofthe preceding claims wherein the solution of the alkaline hydroxide ormixture of alkaline hydroxides contains from 0.1 to 0.5% by weight withrespect to soap of NaCl or of an electrolyte.